Are clozapine blood dyscrasias associated with concomitant medications?

Clozapine is an atypical antipsychotic agent used for refractory schizophrenia. It has a relatively low affinity for D2 receptors and thus is associated with a lower incidence of extrapyramidal side effects when compared with typical antipsychotics. Clozapine as monotherapy can induce a rare, but serious, blood dyscrasia called agranulocytosis; however, some concomitant medications may contribute to the risk. Examples of these medications are mood-stabilizing antiepileptic drugs, such as carbamazepine, and sulfonamide antibiotics, such as sulfamethoxazole. There were no studies at the writing of this article examining the effect of concomitant medications on clozapine blood dyscrasias, and few published reports describing enhanced bone marrow suppression in those taking clozapine. The primary objective of this study was to evaluate the effect of concomitant medications used in a state psychiatric hospital on clozapine-induced blood dyscrasias. This was a retrospective record review of adverse drug reactions reported at an adult inpatient state psychiatric center. The records for a pilot sample of 26 patients with reported clozapine-related adverse drug reactions between January 1, 2007, and June 30, 2009, were reviewed. Fundamental to this study were reported adverse drug reactions defined as 1) substantial drops in white blood cell or absolute neutrophil count (a substantial drop in white blood cell is >3,000 or absolute neutrophil count is >1,500 over a 3-week period); 2) mild leukopenia/granulocytopenia; and 3) moderate-severe leukopenia/granulocytopenia. Concomitant medications were examined for contributions to an increased potential for clozapine-induced blood dyscrasias. Other data collected included demographic information (age, gender, ethnicity), medical and psychiatric diagnoses, dose and duration of medications, and changes in medications. Medications that had a statistically significant impact on the incidence of clozapine-induced blood dyscrasias are reported in this article, as well as the possible duration of medication use prior to induction of an adverse drug reaction.